vaporized/ionized when the lamp is operating. The
The glow lamp consists of two closely spaced
starting gas is neon with small additions of argon, xenon,
metallic electrodes sealed in a glass bulb that contains
or helium. Electrically the LPS ballast is similar to those
an inert gas. The color of the light emitted by the lamp
used with high intensity discharge (HID) lamps. The
depends on the gas. Neon gas produces an mange-red
light produced by LPS lamps is different from the light
light, and argon gas produces a blue light. The lamp
must be operated in series with a current-limiting device
produced by incandescent or fluorescent lamps in that
the color is a monochromatic yellow. All objects other
to stabilize the discharge. This current-limiting device
than yellow appear as various shades of gray. The
consists of a high resistance that is sometimes contained
characteristics of LPS lamps are as follows:
in the lamp base.
The starting time to full light output is 7 to 15
The glow lamp produces light only when the voltage
exceeds a certain striking voltage. As the voltage is
minutes. If a power failure occurs and the power
decreased slightly below this value, the glow suddenly
immediately is restored some lamps may return
vanishes. When the lamp is operated on alternating
to full brilliance; other lamps may take the full
current, light is produced only during a portion of each
half cycle, and both electrodes are alternately
The lamp, has a high efficiency that varies from
surrounded with a glow. When the lamp is operated on
131 to 183 lumens per watt.
direct current, light is produced continuously, and only
the negative electrode is surrounded with a glow. This
The light output cannot be dimmed.
characteristic makes it possible to use the glow lamp as
The fixtures cannot be converted to red or other
an indicator of alternating current and direct current.
colors since the colors other than yellow are not
The glow lamp has five advantages that make it useful
produced by the lamp.
in lighting circuits:
The lamps must be handled, stored, and disposed
1. It is small in size.
of with caution.
2. It is rugged.
3. It has a long life span.
4. It has negligible current consumption.
5. It can be operated on standard lighting circuits.
The LPS lamps contain sodium, a highly
active chemical element, which will oxidize
LOW-PRESSURE SODIUM LAMPS
rapidly and generate a high degree of heat when
exposed to small amounts of water or
Low-pressure sodium (LPS) lamps are installed
moisture-laden air. This could cause a highly
aboard aircraft carriers in special applications (flight
decks and hangar areas). The LPS lamp is characterized
by a large diameter (2 to 3 inches), relatively long arc
The amount of sodium contained in each LPS is
tube that is double backed on itself to save space, with
a two-pin, single bayonet type of base at one end (fig.
small (100 to 1000 mg). The combined number of
4-11). The lamp contains small quantities of sodium
lamps aboard ship could cause a potential hazard if not
handled, stored, or disposed of properly.
which appear as silver-colored droplets that become
Figure 4-11.--A typical low-pressure sodium (LPS) lamp.